XML::Twig::XPath: ' findnodes '仍然抱怨我应该使用' findnodes '而不是' ge

Question

我编写了一些Perl模块来构建XML::Twig树。不幸的是，XML::Twig的XPath实现似乎不完整，所以我加载了XML::Twig::XPath。

由于XML::Twig的文档声明findnodes与get_xpath(在其他几个中)相同，我期望我可以处理像//info_string[text()]这样的查询，而原始XML::Twig不喜欢。

第一次运行时，XML::Twig::XPath抱怨我必须使用getnodes而不是get_xpath，所以我改变了它。

不幸的是，即使在更改之后，我仍然得到相同的消息:

error in xpath expression //info_string[text()] at text()
the expression is a valid XPath statement, and you are using XML::Twig::XPath, but
you are using either 'find_nodes' or 'get_xpath' where the method you likely wanted
to use is 'findnodes', which is the only one that uses the full XPath engine
at /usr/lib/perl5/vendor_perl/5.18.2/XML/Twig.pm line 3566.

我困惑。

下面的语句是这样的:

return $self->_XML()->findnodes($XPath);

_XML()方法返回XML::Twig树，findnodes应该查询该树。

我也试过用use XML::Twig::XPath替换use XML::Twig，但这也没有改变消息。

详细信息由于创建数据结构和从中生成XML的代码过于复杂，因此我将在这里展示XML输出($self->_XML()->print)和数据结构(通过Data::Dumper)。

要查询的XML如下所示:

<MonitoringOutput id="test-id" version="0.1">
<description>This is a test output</description>
<exit_code>0</exit_code>
<status_string>OK</status_string>
<info_string>(demo): Some interesting story</info_string>
<perf_string>L1=0.49 L2=4.7s;;;0;7 L3=0.6;@0.2:0.3</perf_string>
<perf_data count="3">
<sample label="L3">
<label>L3</label>
<value>0.6</value>
<thresholds>
<warn end="0.3" inverted="1" start="0.2"/>
</thresholds>
</sample>
<sample label="L1">
<label>L1</label>
<value>0.49</value>
</sample>
<sample label="L2">
<label>L2</label>
<value unit="s">4.7</value>
<unit>s</unit>
<range max="7" min="0"/>
</sample>
<warn_labels count="0"/>
<crit_labels count="0"/>
</perf_data>
</MonitoringOutput>

这是我尝试做一个可复制的最小的例子:

#!/usr/bin/perl
use warnings;
use strict;
use XML::Twig;
use XML::Twig::XPath;
my $twig = XML::Twig->new();
$twig->parse('<MonitoringOutput id="test-id" version="0.1">
<description>This is a test output</description>
<exit_code>0</exit_code>
<status_string>OK</status_string>
<info_string>(demo): Some interesting story</info_string>
<perf_string>L1=0.49 L2=4.7s;;;0;7 L3=0.6;@0.2:0.3</perf_string>
<perf_data count="3">
<sample label="L3">
<label>L3</label>
<value>0.6</value>
<thresholds>
<warn end="0.3" inverted="1" start="0.2"/>
</thresholds>
</sample>
<sample label="L1">
<label>L1</label>
<value>0.49</value>
</sample>
<sample label="L2">
<label>L2</label>
<value unit="s">4.7</value>
<unit>s</unit>
<range max="7" min="0"/>
</sample>
<warn_labels count="0"/>
<crit_labels count="0"/>
</perf_data>
</MonitoringOutput>');
$twig->findnodes('//info_string[text()]');

当在调试器下运行它时(在不同的机器上使用更新的perl)，我得到以下输出:

error in xpath expression //info_string[text()] at text()
the expression is a valid XPath statement, and you are using XML::Twig::XPath, but
you are using either 'find_nodes' or 'get_xpath' where the method you likely wanted
to use is 'findnodes', which is the only one that uses the full XPath engine
at /usr/lib/perl5/vendor_perl/5.26.1/XML/Twig.pm line 3685.
at /usr/lib/perl5/vendor_perl/5.26.1/XML/Twig.pm line 7122.
XML::Twig::Elt::_croak_and_doublecheck_xpath("//info_string[text()]", "error in xpath expression //info_string[text()] at text()") called at /usr/lib/perl5/vendor_perl/5.26.1/XML/Twig.pm line 7089
XML::Twig::Elt::_install_xpath("//info_string[text()]") called at /usr/lib/perl5/vendor_perl/5.26.1/XML/Twig.pm line 7131
XML::Twig::Elt::get_xpath(XML::Twig::Elt=HASH(0x5591017d3da0), "//info_string[text()]") called at /usr/lib/perl5/vendor_perl/5.26.1/XML/Twig.pm line 3685
XML::Twig::get_xpath(XML::Twig=HASH(0x55910059bb00), "//info_string[text()]") called at /tmp/t.pl line 38

Answer 1

当您构建twig对象时，似乎需要使用XML::Twig::XPath(而不是XML::Twig)。以下内容适合我:

my $twig = XML::Twig::XPath->new();
$twig->parse( .... );
$twig->findnodes('//info_string[text()]');

Answer 2

在构建具有完整XPath支持的XML树时，必须使用XML::Twig::XPath->new构建，并且必须使用XML::Twig::XPath::Elt->new创建添加的元素以使findnodes工作。

由于在我的代码中使用XPath是可选的，所以我决定动态加载XML::Twig或XML::Twig::XPath，这取决于是否需要完全的XPath支持。此外，为了完全支持XPath，我的代码必须使用XML::Twig::XPath::Elt而不是XML::Twig::Elt。

所以我的代码使用了这些技巧:

my $xml_twig = $use_xpath ? 'XML::Twig::XPath' : 'XML::Twig';
my $xml_twig_mod = $xml_twig . '.pm';
$xml_twig_mod =~ s,::,/,g;
require $xml_twig_mod;
my $xml = $xml_twig->new(...);
my $elt = "${xml_twig}::Elt"->new(...);

参见https://stackoverflow.com/a/5790563/6607497